The committee's executive director, Guy Cecil, chimed in with a tongue-in-cheek tweet wondering, "if Linda Lingle would like the cold Colorado winters. She would make a great NRSC recruit there." (Lingle, a former governor of Hawaii, ran unsuccessfully for a Senate seat in the Aloha State in 2012).

But by Friday morning, a fundraising e-mail from Shaheen's husband sent on behalf of her campaign framed Brown's interest in the race as no laughing matter.

"This is serious," Bill Shaheen wrote in a message to supporters. "Brown's campaign spent $40 million in 2012. Most of that went to lie-filled attack ads. He'll try the same thing against Jeanne - and with Wall Street bankers Karl Rove and the Tea Party Super PACs behind him, he could raise even more."

The campaign set a goal of raising $500,000 by midnight on Sunday.

At this point, Democrats have indicated they see Brown less as a "serious" threat to Shaheen and more as a convenient fundraising prop. Within hours of Brown's comment that he was "not going to rule out anything" when it comes to a bid for Senate, Democrats rushed to capitalize on the national attention he would bring to the race.

"Did you hear the news?" asked New Hampshire Democratic Party Chair Raymond Buckley in a fundraising message late Thursday night highlighting the Brown news. "Are you kidding me?!"

(The e-mail message used the subject line "#bqhatevwr," meant to mock Brown for an errant tweet he sent from his iPhone earlier this year.)

Chairman Buckey said on Friday that the Brown news led to the group's "best 12 hours of online fundraising for NH Dems ever." On Saturday night the Democrats are holding a major fundraiser featuring Shaheen, Democratic National Committee Chairwoman Debbie Wasserman Schultz, and New Hampshire's governor and members of Congress.

On Friday, officials from the pro-Democratic group, Emily's List, which lists Shaheen as "top GOP target" on its website, speculated that Republicans were "clearly bored with their own set of subpar options," to run for the seat. (Shaheen was one of the group's first endorsements this year).

"In 2008, Shaheen defeated a sitting GOP senator despite being heavily attacked and outspent," reads a message on the Emily's List site. "Now Republicans are looking for payback - and their right-wing, deep-pocketed allies are gearing up for another spending spree. "

The Cook Political Report rates the seat as "likely" to stay in Democratic hands, but analysts cautioned that a variety of factors "should have Shaheen looking over her shoulder as she gears up to run for a second term."

Brown lost his own Senate race to Elizabeth Warren in November. He told reporters on Thursday that he has long-owned a vacation home in New Hampshire and has "been a taxpayer for 20 years." He would need to change his voter registration in order to run for Senate there.

If the former Massachusetts senator chooses to jump into the race, he's likely to have company from several Republicans who won't hesitate to label him a carpetbagger.

First, there is the man who lost his Senate seat to Shaheen in 2008 - John E. Sununu - and who is said to be considering a bid to recapture the seat. Sununu, however, is ultimately not expected to run.

There are two former members of Congress, Frank Guinta and Jeb Bradley, who appear more likely to challenge the popular incumbent senator. And there are several other wildcards who could be credible contenders.

Brown's attributes, according to one plugged-in New Hampshire Republican include "near universal name I.D." and considerable fundraising prowess. But, the source said that in addition to the reluctance of Granite Staters to accept an outsider, "he would need to navigate a Republican primary, and he would face a Republican primary electorate that is more conservative than a Massachusetts Republican Party electorate."

He is slated to be a keynote speaker at the Grafton County Republican Committee's Lincoln-Reagan Luncheon on April 20. He will also headline the Cheshire County Republican Committee' Lincoln Day Dinner on May 3.